1. Technical Field
The present invention relates to a fluid mixing element which is employed for a static mixer for mixing two or more fluids in the same phase or in different pahses, namely gases, solids (powders or granules) and the like.
2. Background of the Invention
As mixing devices for mixing different kinds of fluids in the same phase or in different phases, various static mixers for mixing the fluids by virtue of their kinetic energies without any other power source have conventionally been proposed.
For example, U.S. Pat. No. 3,286,992 describes such a mixer, which is shown in FIGS. 22 to 24. The Mixer 19 comprises an elongated cylindrical passage tube 17 and short helical blades 18 arranged alternately and in point-contact with each other in the passage tube 17, the contacting edges of each blade 18 being positioned at an angle to those of the adjacent blades.
In such a mixer 19, fluid passages 17a formed in the passage tube 17 are formed in such a manner that fluids A and B which flow through the fluid passages 17a, respectivley, are introduced into the fluid passages 17a of the subsequent blade 18 in the condition that the fluids A and B are divided and mixed by the discontinuous axial displacement of the fluid passages 17a between the blades 18.
However, in the mixer 19 described above, the blades 18 are connected to each other at their contacting edges by welding or brazing. Accordingly, the fluids may stagnate at the junctions.
Further, the fluids A and B are helically rotated so as to follow the profile of the twisted blade 18 described above, because of its helical configuration, and thereby the eddy flow motion of the fluids is caused in each fluid passage 17a. Some degree of turbulent mixing is consequently induced in the passage.
In order to mix the fluids more effectively by utilizing this motion, it is preferable to use the blade 18 twisted at a wider angle. However, special equipment is required, for example, for welding the passage tube 17 and the blades 18 twisted at an angle of 180 degrees as shown in FIGS. 22 to 24.
Next, As an example of techniques for preventing the abnormal stagnation of the fluids which occurs at the junction of the blades previously described, U.S. Pat. No. 4,466,741 describes a mixing element 22 comprising a short passage tube 20 and a helical blade 21 formed in the passage tube 20 so as to be integral therewith as shown in FIGS. 25 to 27. The mixing elements 22 are arranged in a suitable number to be used in such a manner that the contacting edges of the adjacent blades 21 cross at a prescribed angle with the axial displacement as shown in FIG. 27.
In the mixing element 22, fluids A and B are fed into a fluid passage 20a and mixed with each other mainly by virtue of dividing and mixing of the fluids in a similar manner as the invention described in U.S. Pat. No. 3,286,992 stated above.
However, when the mixing element in which the blade is formed integrally with the passage tube is manufactured as shown in U.S. Pat. No. 4,466,741 described above, it is technically difficult to form the element having the blade twisted at an angle of at least 90 degrees by casting or injection molding.
Particularly, it is extremely difficult to form the blade twisted at a wider angle in the passage tube so as to be integral therewith, as shown in FIGS. 22 to 24 described in U.S. Pat. No. 3,286,992.
Further, the dividing mixing which is a main mixing form achieved by the mixing element described in U.S. Pat. No. 3,286,992 or 4,466,741 is inferior in the mixing efficiency. For obtaining the uniform mixture of the fluids finally, therfore, a larger number of mixing elements are required to be connected to each other for use.